Solder has been conventionally used to mount electronic components on a printed circuit board. Since the currently noticeable trend is to avoid using Pb for a solder alloy, solder technique is currently shifting to so-called Pb free soldering in which Pb is not used. Currently, the mainstream Pb free solder alloy includes two types of compositions, that is a tin-silver-copper system and a tin-copper system.
In view of availability of materials, costs of the materials, and reliability of products, the mainstream Pb free solder is the one made of Sn as a main element with an additive metal selected thereto. The inventor of this invention has developed so-called tin-copper solder based on Sn—Cu.
Patent Document 1: Japanese Open Gazette No. 10-107420
Patent Document 2: WO99/48639